	Introduction

Whether many provisions of the Federal Food, Drug, and Cosmetic Act (FD&C Act) apply to a particular drug product turns in part on the novelty of the "active ingredient" of the drug in question.. Alternatively, two drug molecules with the same core compound may have different compounds appended to them by either covalent (i.e., shared electrons) or noncovalent (i.e., no shared electrons) bonds.. As discussed in more detail below, historically, for purposes of the exclusivity provisions, FDA has interpreted "active ingredient," as the term appears in statute, to mean "active moiety," as defined by FDA regulations.. Companies that receive approval for drugs with new active ingredients generally enjoy a competitive advantage in the market while the exclusivity is in effect until generic drugs enter the market.. FDA generally cannot accept new drug applications or abbreviated new drug applications that refer to a drug with NCE exclusivity (i.e., rely on its clinical data and FDA's approval of the drug) for five years.. FDA generally defines active moiety as the core molecule or ion of a drug (i.e., the drug molecule without certain appendages) that is "responsible for the physiological or pharmacological action of a drug substance.". FDA's interpretation has generated disputes between FDA and pharmaceutical companies, as FDA's approach tends to exclude some drugs from being afforded five-year NCE exclusivity under the FD&C Act.. For example, replacing a hydrogen atom in an acid molecule with "a metal or its equivalent" forms a salt, whereas replacing the hydrogen atom with "an organic radical" forms an ester.. For instance, compounds in a final drug product may convert to other compounds through chemical reactions inside the body before arriving at the site of the therapeutic effect, and related but distinct drug molecules may be clinically indistinguishable or convert into the same pharmacologically or physiologically active component inside the body.. Generally, a more expansive interpretation of the phrase "active ingredient," that is, one that considers more types of derivatives to be the same active ingredient, reduces the number of drugs eligible for NCE regulatory exclusivity by expanding the drug ingredients considered previously approved, which, in turn, allows for earlier introduction of generic versions of those drugs.. In 2015, a federal district court rejected FDA's interpretation as inconsistent with the statutory language, though it did not explicitly invalidate FDA's regulations.. In particular, the Food and Drug Administration (FDA) must assess the novelty of the active ingredient in a new drug, comparing it to a previously approved drug's active ingredient to determine whether the new drug qualifies for the five-year "new chemical entity" (NCE) exclusivity.. In the 116th Congress, legislation has been introduced that would generally codify FDA's current approach to evaluating NCE exclusivity and extend that approach to other provisions under the FD&C Act that include the phrase "active ingredient (including any ester or salt of the active ingredient).". The proposed legislation would address those questions by adopting FDA's interpretation.. These derivatives may or may not vary from each other in clinically significant ways, raising the question of which derivative(s), if any, should be considered as the same active ingredient as the core or base molecule.. This process can be technically quite complicated.
Whether many provisions of the Federal Food, Drug, and Cosmetic Act (FD&C Act) apply to a particular drug product turns in part on the novelty of the "active ingredient" of the drug in question. In particular, the Food and Drug Administration (FDA) must assess the novelty of the active ingredient in a new drug, comparing it to a previously approved drug's active ingredient to determine whether the new drug qualifies for the five-year "new chemical entity" (NCE) exclusivity. FDA generally cannot accept new drug applications that refer to a drug with NCE exclusivity (i.e., rely on its clinical data and FDA's approval of the drug) for five years. Companies that receive approval for drugs with new active ingredients generally enjoy a competitive advantage in the market while the exclusivity is in effectâand after, depending how long it takes for generic versions to receive approval once applications can be submitted.
Comparing active ingredients can be technically quite complicated. For instance, compounds in a final drug product may convert to other compounds through chemical reactions inside the body before arriving at the site of the therapeutic effect. In addition, related but distinct drug molecules may be clinically indistinguishable or convert into the same pharmacologically or physiologically active component inside the body. Alternatively, two drug molecules with the same core compound may have different compounds appended to them by either covalent or noncovalent bonds. For example, replacing a hydrogen atom in an acid molecule with "a metal or its equivalent" forms a salt, while replacing the hydrogen atom with "an organic radical" forms an ester. These derivatives may or may not vary from each other in clinically significant ways. This raises the question of which derivative(s), if any, should be considered to be the same active ingredient as the core or base molecule. Generally, a more expansive interpretation of phrase "active ingredient," that is, one that considers more types of derivatives to be the same active ingredient, reduces the number of drugs eligible for NCE regulatory exclusivity by expanding the drug ingredients considered previously approved, which allows for earlier introduction of generic versions of those drugs.
Historically, for the exclusivity provisions, FDA has interpreted "active ingredient" to mean "active moiety," as defined by FDA regulations. FDA generally defines active moiety as the core molecule or ion of a drug (i.e., the drug molecule without certain appendages) that is "responsible for the physiological or pharmacological action of a drug substance." FDA's interpretation has generated disputes between FDA and pharmaceutical companies, as FDA's approach tends to exclude some drugs from being afforded five-year NCE exclusivity under the FD&C Act. In 2015, a federal district court rejected FDA's interpretation as inconsistent with the statutory language, though it did not explicitly invalidate FDA's regulations.
In the 116th Congress, legislation has been introduced that would generally codify FDA's current approach to evaluating NCE exclusivity and extend that approach to certain other provisions under the FD&C Act. This proposed legislation would moot questions about the validity of FDA's interpretation and clarify when chemical entities are sufficiently similar to be considered identical for purposes of drug approval and exclusivity.